Effective September 1st, 2013, support for questions directly related to phpMyAdmin has moved to stackoverflow. All prior support mechanisms have been phased out.
Questions about server issues (web server configuration, "404 - Not Found" error, etc), should be asked on serverfault.com.
The way of reporting (security) bugs and adding feature requests will be unaffected.
We track our issues at GitHub, for code changes you can open pull request there.
If you want to receive commercial support for phpMyAdmin, either as help with installation or implementing custom features, do not hesitate to contact the development mailing list. Please note that these services are not in any way connected with the phpMyAdmin team and we can not guarantee accurate information or quality of service for them.